FIG. 1 shows the structure of a plunger pump of the prior art. This plunger pump acts as a prime mover for a high-speed loom up to 1,000 r.p.m. and is equipped at its one end with a suction ball valve 1 leading to a water source and at its other end with a conduit 3 leading to a water jet nozzle and a high-pressure water flow discharge ball valve or conical valve 2. The water is introduced from the conduit 3 into a cylinder 6, which is actuated by a pump cam lever 5 interlocked with a pump cam 4, by the forward movement of a piston 7 in the cylinder 6. When the pump cam 4 is in an idling position, the piston 7 is moved backwards by the resiliency of a spring mechanism 9 to discharge the introduced water as high-pressure water, and is fed from the conduit 3 through the ball valve or conical valve into the water jet nozzle.
FIG. 2 is a schematic diagram illustrating the pressure waveforms of the water which is discharged from the water jet nozzle unit of the plunger pump for discharging the high-pressure water. The pressure waveforms are ideal if they follow the dotted curve, as indicated, and it is preferable that the time .DELTA.t spent achieving maximum pressure be short and that the fluctuation .DELTA.p at the pressure drop from the maximum level be small.
As a matter of fact, the time .DELTA.t is a factor determined by the relation between the spring pressure and the sectional area of the nozzle jet portion. Therefore, the most important factors for practically establishing the ideal waveforms of high-pressure water are a small pressure fluctuation .DELTA.p and the elimination of the fine fluctuation of the waveforms. For this, it is essential to smooth the movements between the piston 7 and the cylinder 6 and to reduce fluid resistance.
In the high-speed loom, however, the spring pressure of the plunger pump exceeds 200 Kgf, and the clearance between the outer face of the piston 7 and the inner face of the cylinder 6 is formed to have a value of 10/1,000 mm to 30/1,000 mm, taken diametrically. As a result, the piston 7, into which the end of the connection mechanism unit is screwed, is subject to a pulling force towards a pivot pin 11 and the vibration pressure of a rocking mechanism or a spring so that the piston 7 and the cylinder 6 obliquely interfere, as shown in FIG. 3, to cause abnormal wear or to disable smooth movements. Thus, the injected water jet is adversely affected and is subjected to the influences of the flow resistance of the conduit by the disturbances of the discharged water in the conduit, so that the waveforms of the pressurized water are disturbed, as indicated by the solid curve of FIG. 2.
An object of the invention is to provide a structure for a water jet loom plunger pump which will discharge high-pressure water while maintaining the straightness of the piston, thereby retaining smooth movement between the piston and the cylinder.
Another object of the invention is to make it possible to reduce the clearance between the piston and the cylinder by maintaining the straightness of the piston, thereby eliminating the leakage of water from the piston and the cylinder.
Still another object of the invention is to reduce the fine adjustment for retaining the concentricity between the piston and the cylinder and the cost demanded for machining the internal and external diameters of the cylinder to such high precision.
A further object of the invention is to eliminate the defect of the discharged water flowing in a turbulent state into a ball valve or conical valve.
A further object of the invention is to provide a plunger pump which is able to eliminate the fluctuation of the waveforms of the pump water pressure, thereby ensuring a stable and reliable inserted weft at all times by eliminating the dispersion of the maximum water pressure and by minimizing the differential pressure .DELTA.P of FIG. 2.